Casting roll and a method for producing a casting roll

ABSTRACT

A casting roll for the continuous casting of thin metal strips, in particular steel strips in a double-roll or roll-in installation. The roll comprises a roll core with an external casing and an annular roll jacket with an internal casing. The jacket surrounds the core and is being shrunk onto the latter. To prevent migratory motion of the roll jacket in relation to the roll core, the surface of at least one of the opposing casings that form a shrinkage connection has protuberances and indentations, which are oriented at least partially in the direction of the casting roll axis and extend radially for at least 2 μm.

BACKGROUND OF THE INVENTION

The invention relates to a casting roll for the continuous casting ofthin metallic strips, in particular of steel strips, in a two-roll orone-roll casting installation. The casting roll has a roll core with anouter lateral surface and an annular roll shell which surrounds the rollcore, is shrunk on and has an inner lateral surface and having a centralcasting-roll axis, and to a process for producing a casting roll of thistype.

Casting rolls of this type are used to produce metal strip with athickness of up to 10 mm. Liquid metal is applied to the surface of atleast one casting roll, where it at least partially solidifies and isdeformed into the desired strip format. If the metal melt is appliedpredominantly to a casting roll, one speaks of one-roll castingprocesses. If the metal melt is introduced into a casting nip which isformed by two casting rolls arranged at a distance from one another,with the metal melt solidifying at the two casting-roll surfaces and ametal strip being formed therefrom, one speaks of two-roll castingprocesses. In these production processes, large quantities of heat haveto be dissipated from the casting roll surface into the interior of thecasting roll within a short time. This is achieved by the casting rollbeing equipped with an outer roll shell made from a particularlythermally conductive material, preferably copper or a copper alloy, andinternal cooling with a cooling-water circuit. Casting rolls of thistype have already been described, for example in U.S. Pat. No. 5,191,925or DE-C 41 30 202.

U.S. Pat. No. 5,191,925 has disclosed a casting roll in which twoannular roll shells are drawn onto a roll core equipped with coolingducts, and the two roll shells are joined to one another by a weldedjoint, or one roll shell is produced by electrodeposition on the otherroll shell.

DE-C 41 30 202 has disclosed a casting roll in which a join is producedbetween a roll core and a roll shell by brazing, with a suitable brazingsolder, preferably in the form of a strip of this brazing solder, havingto be applied and secured between the roll core and the roll shell priorto assembly. The roll shell is drawn onto the roll core by means of athermal shrinking process and in this way a provisional join is formed,followed by the more time-consuming brazing process.

In conventional continuous-casting installations, it is known for thecontinuous-casting mold to be followed, over the path of the strand, bysupporting and guide rollers, which are subject to significantly lowerthermal loads, for supporting the cast strand (DE-C 40 27 225). In thecase of these supporting and guide rollers, a roller shell is drawn ontoa roller core by means of a shrink-fit connection, with a mating fitwhich complies with the appropriate standards then being providedbetween the roller shell and roller core.

On account of the high productivity required of the installation,extreme cyclical thermal loads are produced at the roll shell of castingrolls for the direct casting of metal strips, in particular when steelis being cast. It is known that a specific dissipation of heat of up to15 MW/m² and more has to be effected through the roll shell. In castingroll structures of the type described in the introduction, which areusually formed by a copper tube shrunk onto a steel core, the local,cyclically occurring circumferential stress fluctuations associated withthe thermal loads give rise to circumferential forces which can causethe copper shell to migrate on the steel core. This migrating movementleads to changes in adhesion at the contact surface between copper shelland steel core, typically leading to rapid aging of the bonded joint. Asa result, the service life of the copper shell or the bonded joint issignificantly reduced.

Even the proposed brazed joint, in addition to being complex to produce,is unsuitable for preventing a migratory movement of the roll shell ofthis type in the long term under the locally high thermal loads whichoccur.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to avoid thesedescribed drawbacks of the prior art and to propose a casting roll and aprocess for producing a casting roll of this type, having a join betweenroll shell and roll core which withstands the high thermal andmechanical loads while preventing migratory movements of the roll shellon the roll core for a prolonged period of time.

In a casting roll of the type described in the introduction, this objectis achieved by virtue of the fact that at least one of the lateralsurfaces which lie opposite one another and form a shrink connection haselevations and depressions in the lateral surface, at least some ofwhich are oriented in the direction of the casting-roll axis and theradial extent of which is at least 2 μm. The elevations and depressionson the lateral surface form supporting surfaces which are predominantlyoriented substantially parallel to the casting-roll axis and, having aminimum radial extent, produce an additional resistance to a migratorymovement of the roll shell with respect to the roll core in thecircumferential direction. With a stochastic distribution of thesesupporting surfaces, their radial extent corresponds to a definedroughness R_(z) of 2 μm.

A stable join between roll core and roll shell is achieved if theelevations and depressions form a surface structure on at least one ofthe lateral surfaces which lie opposite one another, in which surfacestructure the lateral surface has a roughness R_(z) of between 2 μm and1500 μm, preferably between 10 μm and 500 μm. With this level ofroughness, it is possible to achieve optimum penetration of theelevations into the opposite lateral surface while the shrink connectionis being produced, so that a sufficiently large overall supportingsurface formed by the individual supporting surfaces counteractsrotation of the shell.

To prevent a migratory movement of the roll shell in the direction ofthe casting-roll axis and to ensure full centering of the roll shell onthe roll core, at least one of the lateral surfaces which lie oppositeone another has elevations and depressions in and directly around acasting-roll plane of symmetry which is normal to the axis,substantially along the entire circumference of one of the two lateralsurfaces, with a radial extent of at least 2 μm, preferably at least 0.2mm, in particular 1 to 15 mm, which are preferably oriented in thecircumferential direction. As an alternative, these elevations anddepressions in and directly around a casting-roll plane of symmetrywhich is normal to the axis, on at least one of the lateral surfaceswhich lie opposite one another, form a surface structure in which thelateral surface has a roughness R_(z) of between 2 μm and 1500 μm.

This effect is achieved optimally if the elevations and depressions formsupporting surfaces which are directed substantially radially and in thedirection of the casting-roll axis and have a longitudinal extent lessthan or equal to the lateral-surface length. Supporting surfacesoriented in this manner are produced, for example, if the lateralsurface is machined in the direction of the casting-roll axis, forexample by knurling. The approximately V-shaped groove formation whichis thereby established on a lateral surface results in a fixed join tothe further lateral surface if the distance between the groove peaks ispreferably between 0.1 and 1.7 mm and the distance between peak andvalley is between 0.06 and 0.8.

Furthermore, it has proven expedient if the roll core and the annularroll shell, in the region of the lateral surfaces which lie opposite oneanother, are formed from materials of different hardness, and at leastthe lateral surface of the component which has the higher lateralsurface hardness is provided with the predetermined roughness. While theroll shell is being shrink-fitted onto the roll core, the roughnesspattern of the harder lateral surface stamps itself into the softerlateral surface, resulting in a full-surface positive microlock, whichis far superior to the frictional lock which can be achieved during thestandard shrink-fitting operation. A difference in hardness between theedge layers in the region of the harder and softer lateral surfacesshould amount to at least 20%, but preferably more than 50%, in whichcontext the hardness of the softer lateral surface should be less than220 HB, preferably less than 150 HB.

As with the described casting rolls of the prior art, it has provenappropriate for the roll core to be made from steel and the annular rollshell to be made from copper or a copper alloy. Forming the roll corefrom steel provides the casting roll structure with the requiredoperating strength, and forming the roll shell from copper or a copperalloy is imperative for sufficient heat to be dissipated from the metalmelt applied thereto.

To enable the shrink fit to be designed for optimum bonding irrespectiveof the materials selected for the roll core and the roll shell, as wellas other influences, it is preferable for a joining layer to be arrangedbetween the roll core and the roll shell, and for the material whichforms the joining layer to be deposited on one of the two mutuallyassociated lateral surfaces. In this case, one of the mutuallyassociated lateral surfaces is provided with the predetermined roughnessor surface structuring, while the material which forms the joining layeris deposited on the other lateral surface. It is preferable for thejoining layer to consist of a metal or a metal alloy, and wear-resistantgranules may be embedded in this joining layer. These wear-resistantgranules comprise grains or platelets of metal oxides, such as aluminumoxide, zirconium oxide or similar materials or mixtures thereof. Thegranules may consist of grains or platelets of carbides, such astitanium carbide, tungsten carbide, silicon carbide or similar materialswith comparable properties or mixtures thereof. Mixtures of metal oxidesand carbides are also expedient. The metal oxides and carbides with ahigh hardness embedded in a basic matrix additionally reinforce theinterlocking between the lateral surfaces. The joining layer may also beformed by a very hard material, for example a plasma ceramic, in whichcase this material has to be applied to one of the lateral surfaces insuch a way that the desired roughness is also established at the sametime. The joining layer preferably has a layer thickness of from 0.05 to1.2 mm. The wear-resistant granules embedded therein have a grain sizeof less than 40 μm, preferably less than 10 μm.

One further embodiment of the casting roll according to the inventionconsists in the roll core, parallel to the casting-roll axis, havinggrooves distributed over its lateral surface, into which groovessecuring bars are fitted, which project at least 2 μm above the lateralsurface of the roll core in the radial direction. The securing barsprojecting above the lateral surface of the roll core are pressed intothe lateral surface of the roll shell during the shrink connection andthemselves form a supporting surface preventing the shell from rotating,and also, by virtue of being stamped into the roll shell, produce anoppositely directed supporting surface therein. It is preferable forthese securing bars to project no more than 1500 μm above the lateralsurface of the roll core, since the extent to which they can be stampedinto the roll shell is limited. If flush contact between the two lateralsurfaces cannot be achieved solely by the securing bars being pressedinto the roll shell, it is preferably also possible to mill shallowindentations of low depth in the roll shell at the locations locatedopposite the grooves in the roll core.

According to a further embodiment, the securing bars project between 500μm and 15 mm above the lateral surface of the roll core in the radialdirection. In this case, grooves are also milled into the inner lateralsurface of the roll shell, these grooves lying opposite the grooves inthe lateral surface of the roll core, with grooves lying opposite oneanother in each case accommodating one securing bar. The flanks of thesecuring bar and the flanks of the grooves form corresponding supportingsurfaces oriented in the direction of the casting-roll axis. Alarge-area shrink connection between the roll core and the roll shell isadditionally possible if the sum of the depth of two grooves is greaterthan the height of the securing bar which they accommodate.

Typical groove depths in the roll core are from 2 to 15 mm and in theroll shell are from 0.4 to 5 mm. The width of the securing bar isbetween 4 and 45 mm, preferably between 5 and 25 mm. It is customary forfewer than 16, preferably fewer than 8 securing bars and grooves to bedistributed over the circumference of the roll core, preferably atregular intervals. At least 3 grooves are required to sufficientlyprotect against rotation of the roll shell if, at the same time, anuneven distribution of forces and stresses in the roll shell is to beavoided. The length of the grooves and securing bars is shorter than thelateral surface length of the roll core. This avoids the risk of thesecuring bars slipping out under operating load.

A process for producing a casting roll which is suitable for thecontinuous casting of thin metallic strips, in particular of steelstrips, using the two-roll or one-roll casting process, which castingroll substantially comprises a roll core with an outer lateral surfaceand an annular roll shell which surrounds the roll core, has been shrunkon and has an inner lateral surface and a central casting-roll axis, ischaracterized in that the lateral surface of the roll core and the innerlateral surface of the roll shell are prepared for joining byshrink-fitting, in that elevations and depressions, at least some ofwhich are oriented in the direction of the casting-roll axis and theradial extent of which is at least 2 μm, are produced on at least one ofthe mutually associated lateral surfaces which form a shrink connection,and in that the roll shell is drawn onto the roll core at a temperaturewhich is higher than that of the roll core. This is then followed bycontrolled cooling of the casting roll to room temperature.

The preparations for forming a shrink connection substantially comprisea mating fit which is matched to the operating conditions of the castingroll being selected and the roll core being produced with acorresponding external diameter and the roll shell with a correspondinginternal diameter. The measure which is crucial according to theinvention in this context involves the formation of one of the twointeracting lateral surfaces with a surface structure in whichelevations and depressions form supporting surfaces which arepredominantly oriented substantially parallel to the casting-roll axisand which have a minimum radial extent in order to ensure a suitableresistance to a migratory movement of the roll shell in thecircumferential direction. It is preferable for an oriented surfacestructure which has a roughness R_(z) of between 2 μm and 1500 μm,preferably between 10 μm and 500 μm, to be machined into the lateralsurface. In this context, it has proven particularly expedient to form asurface structure in which the elevations and depressions which aremachined into at least one of the mutually associated lateral surfacesare produced with supporting surfaces which are directed substantiallyradially and in the direction of the casting-roll axis and have alongitudinal extent less than or equal to the lateral-surface length.

During production of the shrink connection, the oriented surfacestructure machined into one of the lateral surfaces penetrates into thesurface of the opposite lateral surface with a greatly reducedlikelihood of flats being formed if the roll core and the annular rollshell are produced from materials of different hardness, and thecomponent which is formed with a higher lateral-surface hardness isprovided with the predetermined roughness R_(z). The hardness of thecomponent formed with a higher lateral-surface hardness can additionallybe increased by hardening, nitriding, carburization or a similarprocess. This makes it possible to substantially dispense with the needfor an additional coating, which improves the bonding, on one of themutually associated lateral surfaces.

The oriented surface structure or the roughness R_(z) is produced in asimple way by machining of the lateral surface, for example by knurling,forging or milling. In particular in the case of forging or milling inthe direction of the casting-roll axis, it is easy to produce acorrespondingly oriented surface structure with a predeterminedroughness, which has supporting surfaces that are oriented predominantlyin the direction of the casting-roll axis and counteract rotation of theshell.

The bond between the roll core and the roll shell can be additionallyimproved if a joining layer is deposited on one of the mutuallyassociated lateral surfaces, with the predetermined roughnessadvantageously being applied to one lateral surface and the joininglayer being deposited on the other lateral surface in a layer thicknessof from 0.05 to 1.2 mm. The joining layer, formed from a metal or ametal alloy, is preferably applied to the lateral surface byelectrodeposition or plasma deposition. In addition, it is also possiblefor the granules which have already been described above to beincorporated in the joining layer.

A variant on the described process for producing a casting roll with acorrespondingly stable rotation-preventing measure between roll core androll shell, is produced by virtue of the lateral surface of the rollcore and the inner lateral surface of the roll shell being prepared forjoining by shrink-fitting, by grooves being formed on the lateralsurface of the roll core parallel to the casting-roll axis, into whichgrooves securing bars are fitted which project at least 2 μm, preferablybetween 500 μm and 15 mm, above the lateral surface of the roll core inthe radial direction, and by the roll shell being drawn onto the rollcore at a temperature which is higher than that of the roll core, ashrink-fit connection being produced between the securing bars and theroll shell and at least one sealed join being produced between the rollcore and the roll shell. This is then followed by controlled cooling ofthe casting roll to room temperature.

BRIEF DESCRIPTION OF THE DRAWING

Further advantages and features of the invention will emerge from thefollowing description of non-limiting exemplary embodiments, in whichreference is made to the appended figures, in which:

FIG. 1 shows a partial section through a casting roll with the lateralsurface of the roll core formed in accordance with a first embodiment ofthe invention,

FIG. 2 shows a cross section through a casting roll with the lateralsurfaces formed in accordance with a second embodiment of the invention,

FIG. 3 shows a perspective, outline view of the securing bars used inFIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 diagrammatically depicts a partial section through a casting rollaccording to the invention for the continuous casting of steel strips ina two-roll continuous-casting installation. It comprises a roll core 1made from steel, which ends in roll journals 1 a, 1 b for providingsupport in casting-roll bearings (not shown). A cylindrical roll shell 2made from a copper alloy surrounds the roll core 1 and is secured to thelatter in a manner fixed against rotation by means of a shrinkconnection 3. The shrink connection 3 is formed by the outer lateralsurface 4 of the roll core 2 and the inner lateral surface 5 of the rollshell 2, with the two lateral surfaces 4 and 5, by means of adirectional surface structure, producing an increased resistance againstrotation compared to conventional shrink connections. By way of example,it is illustrated in FIG. 1 that the lateral surface 4 is equipped withknurling 6, with the grooves 7 produced by the knurling being orientedin the direction of the casting-roll axis 8 and forming V-shapedsupporting surfaces 9, which extend substantially radially and in thedirection of the casting-roll axis 8 and in large numbers act assurfaces which resist rotation of the roll shell 2 relative to the rollcore 1. A metallic joining layer 10 is deposited, for exampleelectrolytically, on the inner lateral surface 5 of the roll shell 2 andforms a relatively soft layer with a low hardness, into which thestructured outer lateral surface 4 of the roll core 1 penetrates duringproduction of the shrink connection, without significantly changing itsstructure. In addition, granules formed by various metal oxides orcarbides may be embedded in the joining layer, thereby additionallyincreasing the bonding action.

The casting roll is provided with an inner circulating liquid coolingsystem, in which cooling liquid is fed via a central feed line 11 andradial branch lines 12 to annular coolant ducts 13 which have beenmilled into the outer lateral surface 4 of the roll core 1 and isdischarged again via further radial branch lines 14 and a centraldischarge line 15. Heat is extracted from the steel melt applied to thecasting roll surface 16 by means of the coolant circulating through themilled coolant ducts 13, and this heat is dissipated into the coolantthrough the roll shell 2.

FIG. 2 illustrates a cross section through the casting roll with ashrink connection 3 in accordance with a further embodiment of theinvention. The roll core 1, as in FIG. 1, is equipped with a coolantcircuit, which comprises a central feed line 11, radial branch lines 12,radial branch lines 14 and a central discharge line 15. In theembodiment illustrated in FIG. 2, the annular coolant ducts 13 areturned into the roll shell 2. Parallel to the casting-roll axis 8, fourgrooves 7 are milled into the outer lateral surface 4 of the roll core1, and a securing bar 17, which projects a short distance above theouter lateral surface 4 of the roll core 1, is inserted into each ofthese grooves 7. In the same way, grooves 18 of low depth, which arelocated opposite the grooves 7 in the roll core 1 and togetheraccommodate the securing bars 17, are milled into the inner lateralsurface 5 of the roll shell 2. The lateral flanks 19, 20 of the securingbars 17 and the lateral flanks 21, 22 of the grooves 7, 18 milled intothe circumferential cooling fins in the roll core 1 and in the rollshell 2 (in the region of the circumferentially running cooling fins 24)in this case act as supporting surfaces preventing the shell fromrotating.

FIG. 3 shows a perspective view of the securing bar 17. The securing bar17 includes recesses 23 for the coolant to pass through withoutdisruption, these recesses 23 being flush with the annular coolant ducts13 in the fitted position of the securing bar. Recesses 23 arranged nextto and at a distance from one another have coolant flowing through them,in each case preferably in opposite directions, in order to ensureuniform roll shell cooling. This is indicated by arrows.

The scope of protection of the casting roll is not restricted to theembodiments which have been explained in detail, but rather alsoencompasses in particular casting rolls with a roll shell havingsubstantially centrally located axial cooling bores, and casting rollswith trapezoidal-thread-like cooling ducts machined into the roll coreor the roll shell, or casting rolls with circumferential cooling finsmachined into the roll core.

1. A casting roll for the continuous casting of thin metallic strips, ina roll casting installation, the roll comprising: a roll core having anouter lateral surface: an annular roll shell which surrounds the rollcore and includes an inner lateral surface opposite the outer lateralsurface of the core, wherein: the roll shell is shrunk onto the rollcore so that the outer surface of the roll core and the inner surface ofthe roll shell are in contact substantially over the respective entiresurfaces; at least one of the lateral surfaces has elevations anddepressions forming a surface structure thereon having a roughness(R_(z)) on the surface of between about 2 μm and about 1500 μm; and atleast some of the elevations and depressions are oriented in thedirection of a rotational axis of the casting-roll.
 2. The casting rollas claimed in claim 1, wherein the roughness (R_(z)) is between 10 μmand 500 μm.
 3. The casting roll as claimed in claim 1, wherein: theelevations and depressions are in and directly around a casting-rollplane of symmetry which is normal to the rotational axis and issubstantially along the entire circumference of one of the lateralsurfaces with a radial extent of between about 2 μm and about 1500 μm;and the elevations and depressions are oriented in the circumferentialdirection.
 4. The casting roll as claimed in claim 1, wherein theelevations and depressions form supporting surfaces which are directedsubstantially radially and in the direction of the casting-roll axis andhave a longitudinal extent less than or equal to the lateral-surfacelength (L).
 5. The casting roll as claimed in claim 1, wherein: in theregion of the lateral surfaces which lie opposite one another, the rollcore and the annular roll shell are formed from materials of differenthardness, and at least the lateral surface of the core or the shellwhich has the higher lateral surface hardness is provided with theroughness (R_(z)).
 6. The casting roll as claimed in claim 1, whereinthe roll core is comprised of steel and the annular roll shell iscomprised of Cu or a Cu alloy.
 7. The casting roll as claimed claim 1,further comprising a joining layer arranged between the roll core andthe roll shell.
 8. The casting roll as claimed in claim 7, wherein thematerial which forms the joining layer is deposited on a lateral surfacewhich does not have the roughness (R_(z)).
 9. The casting roll asclaimed in claim 8, wherein the joining layer is comprised of a metal ora metal alloy.
 10. The casting roll as claimed in claim 7, furthercomprising wear-resistant granules embedded in the joining layer. 11.The casting roll as claimed in claim 10, wherein the wear-resistantgranules are comprised of metal oxides.
 12. The casting roll as claimedin claim 10, wherein the wear-resistant granules are comprised ofcarbide grains or platelets.
 13. The casting roll as claimed in claim10, wherein the wear-resistant granules have a grain size less than 40μm.
 14. The casting roll as claimed in claim 1, wherein the surfacestructure is formed by: grooves distributed over the outer lateralsurface of the roll core and parallel to the casting-roll axis; andsecuring bars fitted into the grooves, the bars projecting between about2 μm and about 1500 μm above the lateral surface of the roll core in theradial direction; and the securing bars are pressed into the lateralsurface of the roll shell when the roll shell is shrink fitted onto theroll core.
 15. The casting roll as claimed in claim 14, wherein: thesecuring bars project between 500 μm and 15 mm above the lateral surfaceof the roll core in the radial direction; and the inner lateral surfaceof the roll shell includes second grooves which lie opposite the groovesin the lateral surface of the roll core and respective grooves in theopposite lateral surfaces lie opposite one another and the respectivegrooves opposite one another accommodate one of the securing bars. 16.The casting roll as claimed in claim 14 wherein fewer than 16 of thesecuring bars and grooves are distributed over the roll core.
 17. Thecasting roll as claimed in claim 14, wherein the grooves and thesecuring bars have a length along the axis that is shorter than alateral-surface length of the roll core.
 18. The casting roll as claimedin claim 7, wherein the joining layer is deposited on one of the twolateral surfaces.
 19. The casting roll as claimed in claim 7, whereinthe joining layer is comprised of a metal or a metal alloy.
 20. Thecasting roll as claimed in claim 11, wherein the metal oxides comprisealuminum oxide or zirconium oxide.
 21. The casting roll as claimed inclaim 12, wherein the carbide comprises titanium carbide, tungstencarbide or silicon carbide.
 22. The casting roll as claimed in claim 10,wherein the wear-resistant granules have a grain size less than 10 μm.23. The casting roll as claimed in claim 14, wherein fewer than eight ofthe securing bars and grooves are distributed over the roll core. 24.The casting roll as claimed in claim 15, wherein the sum of the depthsof the two respective grooves is greater than the height of the securingbar which they accommodate.
 25. A process for producing a casting rollfor the continuous casting of thin metallic strips, using a roll castingprocess, wherein the casting roll is comprised of a roll core with anouter lateral surface and an annular roll shell which surrounds the rollcore and has an inner lateral surface adjacent to the outer surface ofthe roll core, and is further comprised of a central rotational axis,the method comprising the steps of: preparing at least one of theadjacent surfaces by forming radially extending elevations ordepressions thereon, at least some of which are oriented in thedirection of the casting-roll axis, to define a surface structurecharacterized by a roughness (Rz) of between about 2 μm and about 1500μm, then drawing the roll shell onto the roll core so that the outer andinner lateral surfaces oppose each other, while holding the roll shellat a temperature which is higher than the temperature of the roll core.26. The process as claimed in claim 25 further comprising, producing theelevations or depressions to define a surface structure in which the atleast one lateral surface has a roughness (R_(z)) of between 10 μm and500 μm.
 27. The process as claimed in claim 25, wherein the elevationsor depressions are formed to have supporting surfaces which are directedsubstantially radially and have a longitudinal extent in the directionof the casting-roll axis which is less than or equal to alateral-surface length in the direction of the axis.
 28. The process asclaimed in claim 25, further comprising producing the roll core and theannular roll shell from respective materials of different hardness atleast at the respective lateral surfaces, and forming the predeterminedroughness (Rz) on the one of the roll core and the roll shell having thehigher lateral-surface hardness.
 29. The process as claimed in claim 28,further comprising applying the roughness by knurling, forging ormilling the respective lateral surface.
 30. The process as claimed inclaim 25, wherein the roll core at least at the outer lateral surface isof steel and the annular roll shell at least at the inner lateralsurface is of Cu or a Cu alloy.
 31. The process as claimed in claim 25,further comprising depositing a joining layer on one of the opposinglateral surfaces.
 32. The process as claimed in claim 25, wherein thepredetermined roughness (R_(z)) is applied to one of the lateralsurfaces and the method further comprises the step of depositing ajoining layer on the other lateral surface.
 33. The process as claimedin claim 31, wherein the joining layer is deposited byelectrodeposition.
 34. The process as claimed in claim 31, wherein thejoining layer is deposited by plasma deposition.
 35. The process asclaimed in claim 31, wherein the joining layer is comprised of a metalor a metal alloy.
 36. The process as claimed in claim 31, furthercomprising incorporating wear-resistant granules in the joining layer.37. The process as claimed in claim 36, further comprising the step ofincorporating metal oxides in the joining layer as the wear-resistantgranules.
 38. The process as claimed in claim 36, further comprising thestep of incorporating carbide grains or carbide platelets in the joininglayer as the wear-resistant granules.
 39. The process as claimed inclaim 36, wherein the wear-resistant granules have a grain size of lessthan 40 μm.
 40. A process as claimed in claim 25, further comprisingpermitting the roll shell to cool after being drawn onto the roll core,so that the roll shell is shrink fitted on the roll core, with thelateral surfaces in a substantially flush relationship.
 41. The processas claimed in claim 30, wherein the roughness is formed on the outerlateral surface.
 42. A process as claimed in claim 37, wherein the metaloxides comprise aluminum oxide or zirconium oxide.
 43. A process asclaimed in claim 38, wherein the carbide comprises titanium carbide,tungsten carbide or silicon carbide.
 44. A process as claimed in claim36, wherein the wear-resistant granules have a grain size of less than10 μm.
 45. A process for producing a casting roll for the continuouscasting of thin metallic strips, in a roll casting process, wherein thecasting roll has a roll core with an outer lateral surface and anannular roll shell which surrounds the roll core and has an innerlateral surface and the roll has a central casting-roll axis, the methodcomprising the steps of: preparing at least one of the lateral surfacesof the roll core and the roll shell for joining by shrink-fitting byforming grooves on the outer lateral surface of the roll core to extendparallel to the casting-roll axis; fitting securing bars into thegrooves wherein the grooves and the bars therein are so sized and shapedthat the bars project above the outer lateral surface of the roll corein the radial direction; then drawing the roll shell onto the roll corewhile holding the roll shell at a temperature which is higher than thatof the roll core for producing a shrink-fit connection between thesecuring bars and the roll shell such that the securing bars are pressedinto the inner lateral surface of the roll shell sufficiently that thelateral surfaces are substantially flush with each other; and producingat least one sealed join between the roll core and the roll shell.
 46. Aprocess as claimed in claim 45, further comprising permitting the rollshell to cool after being drawn onto the roll core, so that the rollshell is shrink fitted on the roll core.
 47. A process as claimed inclaim 45, wherein the grooves and the bars therein are so sized andshaped that the bars project between 500 μm and 15 mm above the outerlateral surface.